In the vertebrate photoreceptor system, signal(photon) reception by rhodopsin(receptor) and activation of cyclic nucleotide phosphodiesterase (PDE) (cellular regulator) is coupled by a light-activated GTP binding protein (GTPase). The two processes can be examined separately. We plan to isolate and characterize the coupling protein (GTPase) and study the mechanism of the manifestation of GTPase activity. We then investigate how the GTPase protein activates PDE. We look for a c-GMP binding protein which would mediate between PDE activation and c-GMP modulation of the NA+ permeability of rod plasma membrane. These proteins will be isolated by biochemical procedures involving gel filtration, affinity and ion-exchange chromatography. After necessary components are isolated, attempts will be made to reconstitute a system (artificial phospholipid membrane) that mimics the light-elicited biochemical and physiological responses of the vertebrate photoreceptor. We recently obtained evidence strongly suggesting identity of rhodopsin kinase and a retina specific uveitogenic antigen. Further studies will be made to establish their identity by biochemical means. We then attempt to isolate uveitogenic peptides and determine antigenic determinants (amino acid sequence). The autoimmune disease is caused by the rod protein that is sealed in the eye before the lymphatic system is completed during development. Therefore, immunopathogenicity of other rod proteins (PDE, GTPase, etc.) will also be investigated.